1. Technical Field
The present subject matter relates to predicting reliability failures of semiconductor devices. More particularly, the subject matter relates to collecting test data from burn-in tests of sample groups of semiconductor devices, and then using the data to statistically predict reliability failures within a general population of semiconductor parts.
2. Background
Semiconductor devices may be fabricated on the surface of a semiconductor wafer in layers and later cut into individual dies. The individual dies thus fabricated are subjected to a series of tests to determine if the dies function properly both before and after being cut. These tests are sometimes repeated at several points in the manufacturing process, since the steps involved in cutting and packaging the dies can result in thermal and mechanical stresses which can induce failures of individual dies. The tests are designed to identify parts that are actually failing when tested, a failure sometimes referred to as a “time-zero” failure.
But many failures that occur in semiconductor dies are not “time-zero” failures, but failures that occur later after the dies have been in operation for a short time. These failures, sometimes referred to as “infant-mortality” or “early” failures, are sometimes identified through the use of a “burn-in” process, in which the dies are operated for an extended period (compared to the duration of normal production testing) beyond the electrical and environmental ranges defined by the design engineers for normal operation. This operational test period may identify a significant number of failures, but this is accomplished at the expense of the additional cost of testing, as well as a reduced life expectancy of the dies tested.
Some manufacturers have used a “no burn-in” approach, using time-zero failures to predict early failures without a production burn-in. Using time-zero failures to predict marginal dies, however, does not always predict failures of dies that are defective. These unpredicted “statistical outliers” tend to increase in number as the dimensions of the semiconductor structures within the dies decrease, and are thus not reliably predicted by time-zero-based no burn-in techniques when applied to many of today's sub-micron semiconductor devices.